Many industries are now using a chemical mechanical process (CMP) for polishing certain work pieces. Particularly, the computer manufacturing industry has begun to rely heavily on CMP processes for polishing wafers of ceramics, silicon, glass, quartz, and metals thereof. Such polishing processes generally entail applying the wafer against a rotating pad made from a durable organic substance such as polyurethane. To the pad, is added a chemical slurry containing a chemical capable of breaking down the wafer substance, and an amount of abrasive particles which act to physically erode the wafer surface. The slurry is continually added to the spinning CMP pad, and the dual chemical and mechanical forces exerted on the wafer cause it to be polished in a desired manner.
Of particular importance to the quality of polishing achieved, is the distribution of the abrasive particles throughout the pad. The top of the pad holds the particles, usually by a mechanism such as fibers, or small pores, which provide a friction force sufficient to prevent the particles from being thrown off of the pad due to the centrifugal force exerted by the pad's spinning motion. Therefore, it is important to keep the top of the pad as flexible as possible, and to keep the fibers as erect as possible, or to assure that there are an abundance of openings and pores available to receive new abrasive particles.
A problem with maintaining the top of the pad is caused by an accumulation of polishing debris coming from the work piece, abrasive slurry, and dressing disk. This accumulation causes a “glazing” or hardening of the top of the pad, and mats the fibers down, thus making the pad less able to hold the abrasive particles of the slurry, and significantly decreasing the pad's overall polishing performance. Further, with many pads, the pores used to hold the slurry, become clogged, and the overall asperity of the pad's polishing surface becomes depressed and matted. Therefore, attempts have been made to revive the top of the pad by “combing” or “cutting” it with various devices. This process has come to be known as “dressing” or “conditioning” the CMP pad. Many types of devices and processes have been used for this purpose. One such device is a disk with a plurality of super hard crystalline particles, such as diamond particles attached to a surface, or substrate thereof.
Unfortunately, such abrasive disks made by conventional methods exhibit several problems. First, abrasive particles may dislodge from the substrate of the disk and become caught in the CMP pad fibers. This leads to scratching and ruin of the work piece being polished. Second, the production methods of the past tend to produce disks having abrasive particles that are clustered in unevenly spaced groups on the surface of the substrate. The resultant non-uniform spacing between particles causes some portions of the CMP pad to be overdressed which creates wear marks, while others are underdressed which creates glazing layers. Third, the abrasive particles of these disks are not configured to penetrate the pad to a uniform depth. This non-uniformity creates additional uneven dressing of the CMP pad. Finally, depending on the degree to which the CMP pad is flexible, it may tend to bulge or bubble in front of the initial leading edge of the dresser due to the downward force exerted by the dresser. Such bulging may cause a depression of the pad to occur as it passes under the remaining portion of the dresser, which may in turn, cause the remaining abrasive particles, especially those that are centrally located on the pad dresser to penetrate the pad less deeply or even skip over the pad entirely. This uneven work load on the dresser particles may cause the pad to be unevenly dressed, and may also cause the dresser to wear unevenly and become worn out prematurely.
Yet another disadvantage with modern CMP pad dressers is reduced service life of the pad conditioner. The effectiveness and efficiency of the service of a CMP pad conditioner is determined by its number of working abrasive particles and the amount of work that is experienced by each particle. As noted above, the service life of a pad conditioner can be reduced by an uneven distribution of work load on the superabrasive particles. When a flexible CMP pad depresses under the pressure of a dresser excessive wear may occur on the leading edge crystals of the pad conditioner as they will bear the majority of the work load. Further, the centrally located abrasive particles are prevented from receiving an equal work load. This work load mismatch increases the wear rate on the leading edge particles and can cause the dresser to become unusable long before the exhaustion of the centrally located particles.
With respect to particle retention, two factors tend to cause the abrasive particles to dislodge from the pad dresser disks of the prior art. First, dislodging often occurs due to the inferior method by which the abrasive particles have been attached. Abrasive particles held to the substrate only by electroplated nickel or other overlay materials are secured only by weak mechanical forces and not by any form of chemical bonding. Hence, these particles become easily dislodged upon exposure to strong mechanical forces such as friction. Furthermore, particle dislodging is facilitated by the chemical attack on the electroplating material which is presented by the chemical slurry.
In contrast, when the abrasive particles are brazed onto the substrate, a chemical bond holds the particles more firmly. However, the acids of the chemical slurry can quickly weaken the braze-particle bonds and dislodge the abrasive particles under the friction of pad dressing. Therefore, to minimize the exposure of the braze to the chemicals and extend the useful life of the pad dresser, the polishing processes must be halted while dressing occurs. The resultant sequence of alternating polishing and then dressing wastes time, and is inefficient.
Warping of the pad dresser working surface during the brazing process also often causes abrasive particles to dislodge. During the brazing process the pad dresser must be exposed to very high temperatures. Exposure to this extreme heat can cause the working surface of the pad dresser to warp, thus compromising the smoothness and planarity of the pad dresser's working surface. As a result, the braze portion of the working surface will be rough, having high and low spots. Such spots are undesirable, as they may cause the braze to begin flaking off, and making micro-scratches on the polished surface of the work piece. Further, such unevenness may cause issues with further processing of the dresser, and abrasive particle retention.
In view of the foregoing, a CMP pad dresser that is constructed and configured to achieve optimal dressing results, with maximized efficiency and lifespan continues to be sought.